During the past few decades, there has been an increasing interest in electronic devices, such as power supplies for various applications. The increasing demand for power supplies has resulted in the continuous development of battery packs, e.g., rechargeable battery packs.
A battery pack can consist of multiple battery cells coupled in series. When one of the battery cells is damaged, the lifetime of the battery pack will be shortened. An unbalance between any two of the battery cells can lead to a reduction in battery lifetime. FIG. 1 illustrates a block diagram of a conventional lead-acid battery pack 100. The lead-acid battery pack 100 is generally employed in low cost applications due to its simple structure. Other battery packs can also utilize lithium ion (Li-ion) batteries.
The battery pack 100 can include multiple battery modules 101-104 coupled in series. Each of the battery modules 101-104 can also consist of six battery cells 111-116 and two electrodes 120 and 129.
Each battery cell in a battery pack needs to have its cell voltage individually monitored. Such monitoring can allow for precise battery cell charging and discharge control. Such monitoring protects battery cells from being charged or discharged when their current voltage level is “over-voltage” (OV) or “under-voltage” (UV). When the voltage of a battery cell, especially lithium ion (Li-ion) battery cells, gets too low, there can potentially be issues, such as internal shorting. Therefore, when the voltage level of a battery cell gets too low, ideally charge/discharge control circuitry will prevent any further charging or discharging. Also, if the voltage output of a battery cells gets too high, further charging of the over-voltage cell should be stopped to prevent the over-voltage cells from suffering damage or burning.
Conventional methods use either complicated voltage translators with op-amps and a voltage sense resistor or in the alternative, by making direct use of a metal-oxide-semiconductor (MOS) field-effect transistor's threshold voltage to check if a battery cell's voltage is too low. Such conventional methods may have a high cost and/or may result in increased power consumption. The conventional methods may also be too simple to meet design requirements. Further, when a MOS threshold voltage is used to check an individual battery cell's voltage output, the MOS threshold voltage is not flexible enough to meet differing requirements. Additionally, the MOS threshold voltage can also vary with process variation and with temperature variation, etc.